1. Field of the Invention
The present invention relates to a medical appliance which can be implanted in the body of a living organism, having means for electrically stimulating tissue contractions and a means for detecting stimulated tissue contractions.
2. Description of the Prior Art
A medical appliance in the form of a cardiac pacemaker is disclosed in European Application 0 236 562 having a terminal which carries the stimulation potential and a terminal which carries a reference potential. The means for detecting stimulated tissue contracts has two terminals and forms therefore a signal corresponding to the potential difference between the two terminals. The pacemaker has means for applying the reference potential to the body of the living organism, and a bipolar electrode which has two contact parts which can be brought into contact with the tissue to be stimulated stimulating a tissue contraction the terminal of the means for stimulation which carries the stimulation potential is connected to at least one of the two contact parts of the electrode and the terminal of the means for stimulation which carries the reference potential is connected to the means for applying the reference potential, and following stimulation one of the terminals of the means for detecting stimulated tissue contractions is connected to one of the two contact parts of the electrode.
More specifically, the aforementioned known cardiac pacemaker has means for stimulating the cardiac tissue, connected on the output side via a terminal which carries the stimulation potential to a first contact part at the distal end of the electrode and via a terminal which carries a reference potential to the housing of the cardiac pacemaker. Corresponding means are connected on the input side to the reference potential, to a second, annular contact part of the bipolar electrode, on the other, in order to detect the reaction of the heart to the stimulation (stimulation response). Due to the fact that the first contact part, to which the stimulation potential is applied, and the second contact part, which detects the stimulation response, are preferably arranged at a distance from one other of at least 0.5 cm, there is a reduction in the superimposition of the detected stimulation response by means of the polarization phenomena produced around the first contact part during the preceding stimulation in the tissue region.